The invention pertains to a device for producing tubes for packaging tubes, comprising an elongated mandrel, around which a substrate web that comprises, in particular, at least one plastic film and a metal foil and/or a metallization can be formed in order to produce a tubular form that surrounds the mandrel and can be conveyed along the mandrel in a conveying direction, as well as welding means for welding the substrate web along a welding region of the tubular form in order to produce a welding seam, wherein the welding region is formed, for example, by an overlapping region produced between two longitudinal edges of the substrate (by two parallel longitudinal edge regions) or alternatively, for example, by two abutting surfaces (contact surfaces) on the longitudinal edges of the substrate web. The invention furthermore pertains to a method for producing tubes for packaging tubes, preferably by means of an inventive device, wherein a substrate web is formed around an elongated mandrel in such a way that the substrate web surrounds the mandrel in order to produce a tubular form, and wherein the substrate web is welded along a welding region in order to produce a welding seam.
Crease formation occurs on the welding seam, in particular, of tubes that are produced of a substrate web that comprises a metal foil and/or a metallization layer in addition to at least one plastic film, wherein this crease formation is undesirable because it affects the optical or aesthetical appearance of the tube body and therefore of the finished tube. Creases or depressions that are spaced apart in the axial direction and extend transverse to the longitudinal direction of the tube, i.e. in the circumferential direction, are typically formed in the welding seam during the welding process.
Another problem in the conception and manufacture of devices for producing tubes can be seen in that the mandrel used, around which the substrate web is formed, for example, with the aid of concave rollers in order to produce the tubular form, needs to be exactly dimensioned with respect to its diameter because the mandrel diameter defines the inside diameter of the tube and therefore the filling volume. The manufacture of the mandrel is very costly because the mandrel needs to have an extremely high resistance due to the abrasive effect that occurs when the tubular form is conveyed along the mandrel in the conveying direction. Even the slightest deviations from the nominal geometry lead to the rejection of the mandrel. The aforementioned problem exists regardless of the substrate structure, i.e. it concerns substrate films with a metal layer or metallization, as well as substrates that consist entirely of plastic.
WO 2009/034485 A1 discloses a method for producing tubes with round cross section, wherein this method aims at elongating a welding seam in the conveying direction of the tubular form or perpendicular thereto, i.e. in the circumferential direction. In this case, it is necessary to arrange corresponding means for elongating the welding seam downstream of a welding device referred to the conveying direction of the substrate in order to ensure at least partial cooling of the substrate prior to the elongation as disclosed in the master claim of the application, wherein this at least partial cooling of the substrate is required for producing a welding seam that should then be longitudinally and/or laterally elongated. This publication addresses the optimization of the roundness of tubular bodies, but not blemishes of a welding seam to be produced.
US 2010/000674 A1 discloses a method and a device for producing tubular bodies, wherein the method and the device aim at respectively connecting the longitudinal sides of the substrate material indirectly or not only by fusing the substrate material.
In fact, a separate fused-on plastic strip is used for connecting the longitudinal edges of the substrate web to one another. In the known device, the tube diameter and its circumference are respectively defined by the width of the substrate web and the spacing of the longitudinal edges of the substrate web only. The known device features height-adjustable moulding means in order to respectively adjust the thickness of the welding seam or of the additionally fused-on plastic material after a definitive adjustment of the tube diameter. In this case, the moulding means operate in a stress-free fashion referred to the circumferential direction of the tubular form produced. The radial adjustability of the moulding means is limited by an outer ring and the plasticized mass accommodated between the ring and the moulding means such that the moulding means cannot be adjusted beyond the outer circumference of the mandrel.